While Miah and I had the engine out to do the core plugs, it looks like the torque converter's fallen off the gearbox a bit. Any hints on getting the splines lined up properly so I don't wreck the pump when I refit it?

I've always jammed a bit of wood in through the hole at the bottom of the bellhousing but it's a bit late now. RAVE says to stand the gearbox on end and rotate it as it drops straight down and meshes with the splines. But, if you don't fancy dropping the gearbox, I'd say just take the weight and rotate it a bit and see if you feel it slot in.

The spin and wiggle technique is the one to use..

When it's fully seated you'll hear the pump click when you rotate it..

Rotate with a bit of light pressure, it will find the pump drive and locate easily,, nothing to worry about..

Once it finds the pump drive and fully seated use some rigi-foam or similar material to keep it tight in place. If you don't fix it properly you are going to damage the pump. Once you align the engine and about to fit the bell housing bolts you can rotate the TC through bottom opening to align the TC bolts with end plate, if required.

It did indeed slot back into place with a particularly satisfying "thunk", with a bit of turning and jiggling. When it's not fully on the splines it's quite wobbly on the shaft, and once it's on properly it's quite clearly "happier".